Broad band coaxial line to wave guide coupler



Oct. 24, 1950 w. w. MUMFORD 2,527,146

BROAD BAND COAXIAL LINE T0 WAVE GUIDE COUPLER Filed March 27, 1945 I0 F/G. ,L

SIGNAL 9 sou/ace Fla 4 FIG 5 l/VVENTOR W W MUMFORD A TTORNE Y Patented Oct. 2 4, 195

BROAD BAND COAXIA'L LINE .ToWAv GUIDE GOUPLER William W. Mumford, Shrewsbury Township,

Monmouth County, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York,

N. Y., a corporation pf N ew York v ApplicationMarch 27, 1945, ser 11v sa09e This invention relates to transmission eoupling apparatus, and particularly to a coaxialline-towave guide transducer for use in a multifrequency microwave signaling system.

Heretofore in microwave signal systems, ;a tuner of the piston type has been embodied in a wave guide for matching the impedance of the wave guide and that of the coaxial conductor line connected therewith. Such piston tuning tends to provide the system substantially with a single frequenc versus impedance characteristic. In other words, the frequency versus impedance characteristic of the coaxial-to-wave uide coupling tends to peak sharply at a particular op: erating frequency. Hence reflection effects tend to be introduced in the signal system as the operating frequency varies from the particular frequency; This requires, at least, tuning the system for each different operatin frequency. One way proposed heretofore to evercome such single frequency characteristic has been te extend the bare inner conductor of the cQaxial cone ductor line entirely across the interior of the Wave guide so that the free end of the inner con.-

ductor projects outside the wave guide. This tends to provide the coaxial-to-wave guide couplingwith a frequency versus impedance char acteristic which was substantially ,flat ,over a limited band width.

The present invention contemplates a coaxial 1ine-to-wave guide transducer provided with-. a frequency versus impedance characteristicwhich is substantially flat over a wider band width than any obtained heretofore.

The main object of the invention is to match the impedance of a coaxial conductor line and a wave guide over a broad band of signal frequencies.

Another object is substantially to eliminate reflection effects over a broad band of signal frequencies.

In a specific embodiment of the present invention which is disclosed in connection with a con-, Ventional microwave signaling system described hereinafter, the inner conductor of the coaxial line and the insulation thereon areextended substantially one-fifth (wavelength in the interior of the wave guide, each endwall of the wave guide has its inner surface located substantially onefifth guide-wavelength from the vertical axis of the inner conductor positioned in proximity of each end wall, and'a vertical plane embodyinga vertical axis of the inner conductor. is spaced from a vertical plane includingthe longitudinal .axis of the waveguide. Ithas been found'in prac- 2 cs that thi aQ X V Ji'tQ WaVB. gu e upli is previded; with a substantially flat frequency vers moedanes c a a t st c f a per ent b nd ate-fr uen o th der of 3.000 es Cycl ssu anti y on -q ar r wavel h f om the v rtica axi of heoinns conduct r n s o n ro m th reof. a a t a Pl n em yng-the ertical a is f the inner c ndu coin ideswithaverti e lan udi the loneii tudinal axis of the wave guide. ,It has beenfound in p a c a hi Q s sl-tO-W v u d .69 pling exhibits a substantially fiat frequency versus impedance characteristic for a :12 per cent band at a frequencyof the order of 3, 000 megacycles,

In bothforegoing embodiments of the inven; tion, a tuning. plug is, or may be provided, movably mounted in one wall of thewave guide in axial alignment with the dielectric-covered inner cone ductor. A further embodiment of the invention concerns the extension of the insulation-covered inner conductor'entirely across the interior of the waveguide, and the mounting ofa tubular tuning plug in a movable mannerin a ,wall of the wave guide in proximit of the, free end of the insulation-covered inner conductor and in coaxial relation therewith. Such tuning plugs pr'ovide a, varie able capacity effect which tends to nullify any inductive effect inherent in the in sulation-covered inner cojnductors, and thereby further tends towiden the frequenc VQ SHS impedance charac teristics ,ofthe coaxial-to-wave guide coupling.v

The invention wil hereadily understood from the followingdescription taken together with the accompanyin drawing, in which: I

Fig. 1 is a schematic circuit diagram of a micro wav s enali ss sm il u tratin hs s fic m-i bod me' ofthenvsntisnan sh w nava lsvae tional view of the wave guide element partly in cross-section; I v

Figs. '2 and 4. ar frasm nta ynlan vviews :of the wave guide element in Fig.1 shown partly in cross-.- sec'tion;

Fig. 3 is a fragmentary ,yiew of the wave guide element ,of Fig. 1, showing a modification .of the invention, and

Fig.- 5 is a fragmentary viewv of the ,wave guide element ,of Fig. 1 showing a further modification of theinvention. Herein, the term ..f.waveleng th? employed to identify the length of a dielectric-covered inner conductor in the interior of a wave guide relates to wavelength in free air; the term guide-wavelength designates distance in the interior of the wave guide; and the term microwave denotes a, wave having a length less than one meter, and as short as one centimeter or one millimeter.

One known device for coupling a coaxial line to a wave guide and utilizing pistons for tuning such device to a particular operating frequency, and another known coupling device for the same purpose and extending a bare inner conductor of the coaxial line entirely transversely of the interior of the wave guide to establish a substantially flat frequenc versus impedance characteristic over a limited frequency range in such coupling device are both disclosed in the copending application of A. C. Beck, Serial No. 429,358 filed February 3, 1942, which has matured into Patent No. 2,408,032 granted September 24, 1946. e

Referring to Fig. 1, a source In of signal microwaves extending over a preselected frequency range is connected to an inner conductor II and an outer conductor I2 both of which constitute a coaxial conductor line 9. At the left-hand end of wave guide I3, the outer conductor I2 is electricall connected thereto, and a, portion I4 of the inner conductor II covered with a suitable dielectric I'I extends into the interior of the wave guide I3 through an opening in the upper side wall thereof. The dielectric-covered portion I4 serves to effect transmission between the coaxial line 9 and Wave guide I3 in the well-known manner. At the right-hand of wave guide I3, a similar coaxial line 8 effects transmission between wave guide I3 and load I5.

In accordance with the present invention as illustrated in Fig. 1, the portion I4 and the dielectric I'I thereon are both extended a distance a into the interior of wave guide I3, and the vertical axis of the dielectric-covered portion I4 is located a distance D from the inside surface of left-hand end wall I6 of wave guide I3. Referring to Fig. 2, the vertical axis of the dielectriccovered portion I4 lies in a vertical plane which is spaced a distance d from a vertical plane through the longitudinal axis of wave guide I3. The foregoing structure is duplicated for the coaxial line 8 and end wall I located at the right-hand end of wave guide I3.

In one embodiment of Figs. 1 and 2, the size of the wave guide I3 was 1%; by 2 /2 inches, and the coaxial lines 8 and 9 individually included an inner conductor II of No. 22 AWG tinned copper wire, an outer conductor I2 of two braided shields of No. 36 AWG tinned copper wire, and a dielectric ll of low capacity rubber of approximately 0.196 inch in diameter enveloping the inner conductor and concentrically spacing the inner and outer conductors. The source 10 supplied microwaves having a wavelength in the range of 9.0 to 10.95 centimeters. It has been found in practice that the distance a for the dielectric-covered portion I4 in the interior of the wave guide was of'the order of one-fifth wavelength, and the distance 12 for the location of the end walls I6 and I6 with reference to the respective dielectric-covered portions I4 was of the orderof one-fifth guidewavelength. This embodiment was found to provide a substantial impedance match for microwaves in the wavelength range of 9.0 to 10.95 centimeters with a reflection loss of less than 0.02 decibel. This involved a' frequency range of the order of :9 per cent relative to the mid-frequency of the transmitted band. Accordingly, the embodiment of the coaxial-towave guide transducer of Figs. 1 and 2 had a frequency versus impedance characteristic which was substantially fiat over a band of approximately 600 megacycles in a preselected frequency range of the order of 2,740 to 3,333 megacycles.

In Fig. 3 a tuning plug I9 is disposed in a lower side wall of wave guide I3 which is opposite to that through which the dielectriccovered portion I4 extends. The plug I9 has an axis in diametrical alignment with an axis of the dielectric-covered portion I4, and is preferably provided with a cross-section which is substantially equal to that of the dielectric-covered portion I4. The plug I9 is movably mounted in a suitable manner in the wave guide I3, and adjustments of its position serve to vary the distance and thereby the effective capacity between the inner surface of the wave guide I3 and the adjacent end of the dielectric-covered portion I4.- This tends to nullify any inductive effect inherent in the dielectric-covered portion I4. The amount of the plug adjustment depends on the relative cross-sections of the dielectriccovered portion I4 and plug I9. A nut 20 maintains the plug I9 in place after individual adjustments thereof. Thus, the plug I9 tends to widen still further the frequency versus impedance characteristic obtainable in Figs. 1 and 2.

In another embodiment of Fig. 1, the vertical axis of the dielectric-covered portion I4 is located in a vertical plane which coincides with a vertical plane'embodying the longitudinal axis of the wave guide I3 as shown in Fig. 4. The source I 0 now supplies microwaves having a wavelength in the range of 8.94 to 11.4 centimeters. The size of the wave guide I3 is 1 /2 by 3 inches. The coaxial conductor lines are identical with those mentioned above. It has been found in practice that the distance a for the dielectric-covered portion I4 in the interior of the wave guide I3 was substantially 0.214 wavelength, and the distance b for the location of the end walls I6 and I6 with reference to the respective dielectric-covered portions I4 was substantially 0.223 guide-wavelength. This embodiment was found to provide a substantial impedance match for microwaves in the wavelength range of 8.94 to 11.4 centimeters, with a reflection loss of approximately 0.033 decibel. This involved a frequency band of the order of :12 per cent relative to the mid-frequency of the transmitted band. Thus, the embodiment of the coaxial-to-wave guide transducer of Figs. 1 and 4 had a frequency versus impedance characteristic which was substantially flat over a band of approximately 730 megacycles in a preselected frequency range of the order of 2,630 to 3,360 megacycles. The tuning plug I9 in Fig. 3 may also be used with Figs. 1 and 4 as desired.

The dimensions a and b in Figs. 1, 2 and 4 may increase or decrease from the foregoing specified distances depending on the frequency range of. the transmitted signals, the variations of the sizes of the wave guide and/or the cross-section of the dielectric-covered portion of the inner conductor in the interior of the wave guide, and the on or off-center location of the dielectriccovered inner conductor with reference to the longitudinal axis of the wave guide. It has been found in practice that for Figs. 1, 2 and 4 the ter wavelength, and the dimension b varied ap- "proximately betweencone-seventh 1 and *one-zquarfrequency versus impedancenharacteristics .men-

tlonedihereinbefore.

In Fig. 5 the inner conductor 25 and :solid dielectric 26 thereon areextendedientirely- :across the interior of the wave. guide :21 so that the lowermost .:ends :of bothlthe inner conductor :and dielectric 'lie exteriorlyof -;the outer surface of the wave guide. 'A tubular metaIIicJmember rs suitably mounted in the wave guideis disposed coaxially'with the lowermost end of ztheidielectric covered winner conductor. Adjustments got the position of. the .member .28 relative to :the end of the dielectricecovered inner conductor tend to vary-j the effective capacity between the wave guide and the inner .conductorand diel'ctric. This tends to .nullifyiany inductive efict inherent in the inner conductor and dielectric in the interior of the wave guide. A nut 29 holds the member.,28 inposition aftereach adjustment. The arrangement of Fig. ;5 maybe substituted for th e coaxial conductor lines of Fig.1.

In Fig. 1, for rectangular wave guides-haying the dimension ratio of :oneto'two, for example, Ayby 1 A, by 1, l by 2 /2, 11/2 by;'3:,inches, etc., the distance d can be determined fairly closely with the following equation:

Z W where Z0 is the characteristic' impedanceof the coaxial line 40, d is the distanceoff-center, W is the width (inside dimensionipf the wave guide M, A 'the wavelength of the wave lying in the middle of the transmitted band, (LA and W'being in like units. This equation may be used for determining the oif-center location of the portion I4 in Fig. 1.

What is claimed is:

1. In combination, a wave guide, and a coaxial line having its outer conductor connected to said guide and its inner conductor extending into the interior of said guide through an opening in one side wall thereof, said inner conductor being imbedded in a solid dielectric substantially throughout its entire length in the interior of said guide, and said inner conductor being positioned off the longitudinal axis of said guide.

2. In combination, a wave guide, a coaxial line having its outer conductor connected to said guide and its inner conductor extending into the interior of said guide through an opening in one side wall thereof and terminating in"the interior of said guide, and a solid dielectric gripping substantially the entire longitudinal surface of said inner conductor in the interior of said guide, said inner conductor and said dielectric thereon eXtending into the interior of said guide to a distance lying between one-seventh and one-quarter wavelength, and said inner conductor having its vertical axis lying in a vertical plane spaced from a vertical plane embodying the longitudinal axis of said guide.

3. A combination according to claim 2 in which said inner conductor has its vertical axis lying in a plane which coincides with a plane embodying the longitudinal axis of said guide.

4. In combination, a wave guide, a coaxial line having its outer conductor connected to said guide and its inner conductor extending into the interior of said guide through an opening in one of :asald; guide, .a :solid "dielectric "engaging-substantially "the .entirev length-wise 'arealof said inner conductorlinxtheinterior of. said. guide, and

,a :wall for closing the end-.of ssaid guideinzproximityof'said inner conductor, said end wallihav ing :its inner surface located adistance which is greater than once-seventh guide-Wavelength but; less thanone-quarter guide-wavelength :from an :axis of said innerconductor. a

5. A signal system comprisingiaiwave guide; a.walliforlclosing.one end ofsaid wave .=guide,.an electrical :apparatus, ":a .coaxial conductor-line COlII'IBCtEdTtO saidapparatus, said line havinglits outer conductor connected tozsaid. wave guide improximityaof said-one end thereof/and its'inner conductor extending into the -interior-.of said wave guide through an openingtin -.one-.side::wall thereof and terminating in the: interior :of said guide, asoliddielectric substantially surround-'- ingwsaid inner. conductor in saidzwave :guide,.iand meansfor providing said system with"a' substantiallyiflatffrequency versus impedanceycharaicter; istic over a band width of at 1east 600 megacycles in apreselectedirange' ofthe frequencies of the jsignaling waves being transmitted in said system, comprising said inner conductor and dielectric extending substantially one-fifth wavelength in the interior of said wave:guide,';said aend wall having its inner surface :located substantially one-fifth guide-wavelength from the vertical axis of :said inner conductor, and :said inner conductor having its verticalsaxisilying ina vertical plane spaced-from a vertical plane embodying the longitudinal axis of said wave-guide;

.6. A circuit :comprising'a waveguide, a wall for closing-:one endof said waveguide, electrical apparatus for waves whose frequencies extend over abroad band, a coaxial conductor line having its inner and outer conductors connected to said apparatus, said line having its outer conductor connected to said wave guide in proximity of said one end wall and its inner conductor projecting into the interior of said wave guide through an opening in a side wall thereof and terminating in the interior of said guide, a solid dielectric substantially surrounding said inner conductor in the interior of said guide, and means for providing said circuit with a substantially fiat frequency versus impedance characteristic 7 over a band width of at least 730 megacycles in a preselected range of the frequencies of the signaling waves being transmitted in said circuit, comprising said inner conductor including said dielectric thereon projecting substantially onefifth wavelength in the interior of said wave guide, said end wall having its inner face located substantially one-quarter guide-wavelength from the vertical axis of said inner conductor, and said inner conductor having its vertical axis disposed in a vertical plane coinciding with a vertical plane embodying the longitudinal axis of said wave guide.

7. In combination, a wave guide, a coaxial line and its inner conductor extending across the interior of said guide through diametrically aligned openings in opposite side walls thereof, said inner conductor being entirely surrounded with a solid dielectric along its axial length, and a hollow conducting member movably mounted on one side wall of said wave guide in coaxial relation with the free end of said inner conductor.

8. In combination, a wave guide, a coaxial line having its outer conductor connected to said guide and its inner conductor extending into the interior of said guidethrough an opening .in one side wall thereof, a solid dielectric engaging substantially the entire longitudinal area of said in? her conductor in the interior of said guide, and a member movably mounted in a further, side wall of said guide, said further side wall beingopposite said one side wall, said innerconductor and memher having axes in diametrical alignment, said member being movable along its axis aligned with said inner conductor.

9. In combination, a wave guide, a coaxialline comprising an outer conductor connected to :said guide and an inner conductor extending into the interior of said, guide through an opening in a side wall thereof, a non-conductive sleeve engagingsubstantially the entire length-wise surface or said inner conductor in the interior, of said guide, and a wall for closing the end of said guide nearest to said inner conductor, said ;wall having its :inner surface spaced from: an' axis of. .said inner conductor a distance which is at least-ape proximately tone-seventh 'but substantially less thanone-quarter guide-wavelength at the-mid,- irequency of the frequency band of signaling waves transmitted in said guide.

, 10. .A combination according to claim 1 which includes a member movably mounted in a side wall of said guide opposite said one side Wall, said inner conductor and member having axes in alignment, said member being movable with respect to said inner conductor along its axis aligned with said inner conductoni i a 11. A combination according to claim 1 which includes said inner conductor terminating in the interior. of said guide, and amember movably mounted in .a side wall of said guide opposite said one side wall,,said inner conductor and member having axes in diametrical, alignment, said member being movable with respect to said inner conductor along its axis aligned with said inner conductor: '12. A broad band coupler for wave guide of elongated rectangular cross section and a coaxial line having a solid dielectric filling the space between its inner and'outer conductors, comprising a reflecting-barrier in said guide, said line haviing its outer conductor connected to and terminating at a broader side wall of said guide. ad jacent said barrier and its inner conductor projecting 'into the interior of said guide and ter minating =therein, said dielectric continuing into thein'terior of said guide as a sheath for said projecting inner conductor, said last-mentioned dielectric being substantially coextensive with said projecting inner conductor, and said inner conductor being positioned substantially of! the center o'fsaid broader side wall. i WILLIAM W. MUMFORQ':

, REFERENCES CITED The following'referenc'es are of record inthe file of this patent: I UNITED STATES PATENTS Date Number Name 2,106,769 Southworth Feb. 1, 1938 2,128,235 Dallenbach Aug. 30, 1938 2,219,653 Krugel Oct. 29, 1940 2,282,856 Engbert- May 12, 1942 2,311,520 Cliflord Feb. 16, 1943 2,404,086 Okress July 16, 1946 2,408,032 Beck Sept. 24, 1946 2,431,941 Kihn Dec. 2, 1947 f FOREIGN PATENTS Number 1 Country Date 116,110 Australia Nov. 4, 1942 

